MITT ROMNEY: It's an honor to announce my running mate and the next vice president of the United States, Paul Ryan.

(SOUNDBITE OF CHEERING)

RAZ: That's Mitt Romney, ending weeks of feverish speculation earlier today. Wisconsin Congressman Paul Ryan, the chairman of the House Budget Committee, has joined the GOP presidential ticket. The two men launched a multiday, multistate bus tour that kicked off in Norfolk, Virginia, this morning where Paul Ryan spoke to energized crowds.

PAUL RYAN: Our rights come from nature and God, not from governments.

(SOUNDBITE OF CHEERING)

RYAN: That's right. That's who we are. That's how we built this country. That's who we are.

UNIDENTIFIED GROUP: USA, USA, USA, USA...

RYAN: That's what made us great.

UNIDENTIFIED GROUP: ...USA, USA...

RYAN: That's our founding.

RAZ: Romney's choice is being heralded as a bold one. Paul Ryan is controversial, not least for his plan to privatize Medicare and Social Security. In a few moments, we'll head to the campaign trail, and later, how the philosopher Ayn Rand came to inspire Paul Ryan's entry into politics. But first, a question: Who is Paul Ryan? Here's NPR's Brian Naylor.

BRIAN NAYLOR, BYLINE: Paul Ryan remembers his first job in Washington. It came after college. He attended Miami University in Ohio, and he was thinking of taking some time off to do some skiing. Ryan told CNN last year his mother tried to dissuade him.

RYAN: And my mom was worried that if I, after college, went to go do some skiing that it would take two years to turn into five, 10, whatever years. And so I was offered a job as an economics policy researcher for my home state Senator Bob Kasten at the time, and she really gave me a big nudge to take that job because she was worried I'd become a ski bum. And that's when I got involved into economics and politics.

NAYLOR: Ryan was born and grew up and still lives in Janesville, Wisconsin, southwest of Milwaukee. He's Catholic. His father, a lawyer, died when Paul was 16. He grew up fast, he told The New Yorker. He took school seriously, was elected president of the junior class and won the dubious distinction as biggest brown-noser in his senior year.

Ryan's wife, Janna, is a tax attorney and cousin of Democratic Congressman Dan Boren of Oklahoma. The Ryans have three school-age children. Like many Republicans, he's pointed to his family as reason for his concerns about the debt and the size of government. Here's Ryan delivering the Republican response to President Obama's State of the Union address in 2011.

RYAN: On this current path, when my three children, who are now 6, 7 and 8 years old, are raising their own children, the federal government will double in size and so will the taxes they pay.

NAYLOR: In 1998, Ryan ran for the House seat vacated when Republican Mark Neumann ran for the Senate. By all accounts a determined campaigner, Ryan won surprisingly easily and joined the House at age 28. As a congressman elect, Ryan told C-SPAN he couldn't wait to get back to Wisconsin.

RYAN: I'm an avid hunter. I come from Wisconsin. I'm actually - opening day of deer season is Saturday so I'm flying back Friday so I can join my family hunting for deer.

NAYLOR: Ryan quickly rose up the GOP ranks on the strength of his ideas. Among them, a plan to partially privatize Social Security that was adopted by the Bush administration but which died in the face of united opposition from Democrats. Still, by proposing dramatic changes to a program long dubbed the third rail of American politics, Ryan showed his determination to change Americans' relationship to the federal government. It's the kind of change he continues to push as he stated in his speech earlier this year to the conservative political action conference CPAC.

RYAN: Boldness and clarity offer the greatest opportunity to create a winning coalition. We'll not only win the next election; we have a unique opportunity to sweep and remake the political landscape.

NAYLOR: That willingness to be bold contrasts with and may compliment Mitt Romney's more cautious approach to campaigning and governing. It's evident in the budget the House passed this year that Ryan drafted and which would eventually replace Medicare with a voucher-like program. That idea will now become a centerpiece of the presidential campaign and puts Paul Ryan squarely in the middle of a major fight over the future of the nation's fiscal and social policy. Brian Naylor, NPR News, Washington. Transcript provided by NPR, Copyright NPR.